This invention relates to an .alpha.-olefin polymerization catalyst system, a process for producing an .alpha.-olefin polymer using the same, a solid catalyst component for an .alpha.-olefin polymerization, and a process for preparing the same. More particularly, it relates to a novel polymerization catalyst system for polymerizing an .alpha.-olefin which has a very high catalytic activity per solid catalyst and per titanium atom and to a process for producing a highly stereoregular .alpha.-olefin polymer which contains little catalyst residue and little amorphous polymer and which has excellent mechanical properties and excellent processability using the above novel catalyst system.
In the production of a polymer of an .alpha.-olefin such as propylene, butene-1 or the like, it is well-known to use a Ziegler-Natta catalyst consisting of a transition metal compound of Group IV to VI of the Periodic Table and an organometallic compound of Groups I to III of the Periodic Table.
In the production of an .alpha.-olefin polymer, amorphous polymers are produced as by-products in addition to a highly stereoregular .alpha.-olefin polymer which has a high industrial utilization value. Said amorphous polymer is low in industrial utilization value and adversely affects on the mechanical properties required in molding the .alpha.-olefin polymer into a molded article, film, fiber, other processings and using the same. Also, the formation of amorphous polymer brings about the loss of the starting monomers and requires an equipment for removing the amorphous polymer. This is very disadvantageous in industry. Accordingly, the catalyst system for producing an .alpha.-olefin polymer is required to produce no or little, if any, such amorphous polymer. Furthermore, in the .alpha.-olefin polymer obtained, there remains a catalyst residue consisting of the transition metal compound and the organometallic compound. This catalyst residue causes problems in various respects such as stability, processability and the like of the .alpha.-olefin polymer, and hence, it becomes necessary to provide an equipment for removal of the catalyst residue and stabilization of polymer.
The above disadvantage can be overcome by increasing the catalytic activity represented by the weight of the .alpha.-olefin polymer produced per unit weight of catalyst, whereby the equipment for removing the above catalyst residue becomes unnecessary and the cost for producing the .alpha.-olefin polymer can be reduced.
It is known that when a Ti--Mg complex type solid catalyst obtained by reducing a tetravalent titanium compound with an organomagnesium compound in the presence of an organosilicon compound to form a magnesium-titanium eutectic mixture is used in combination with a cocatalyst organoaluminum compound and an organosilicon compound as the third component used in the polymerization, highly active, highly stereo-selective polymerization of an .alpha.-olefin can be realized to some extent (see JP-B-3-43,283 and JP-A-1-319,508).
These cases are in such a level that the realization of an extraction-free, deashing-free process is possible to some extent; however, a further improvement has been desired. Specifically, in order to make the quality of .alpha.-olefin polymer higher, it has been desired to realize a higher stereoselective polymerization without sacrificing the particle size distribution and the like. In particular, in uses in which it is desired for a polymer to have a higher stiffness as in the field of molding, the appearance of a catalyst having a high stereoregular polymerization ability and a good particle size distribution has been earnestly desired because a high stereoregularity of the polymer directly results in a high stiffness product.